In contrast, ultrashort pulses (\(<10\)  ps) lead to limited heat-affected zone. However, permanent modifications are extremely challenging to produce in the bulk and the exit surface of silicon with ultrashort laser pulses [1]}, unless complex approaches are implemented for optimizing the spatial [2]}, [3]}, [4]}, spectral [5]}, [6]}, or temporal [7]}, [8]}, [9]} properties of the irradiation. These limitations originate from the high nonlinear refractive index of silicon (on the order of \(10^{-14}\)  cm\(^{2}\)  W\(^{-1}\)  [10]}, [11]}), which causes micro-filamentation at modest peak powers—and thus, an intensity clamping similar to that described for transparent media [12]}, [13]}. The main difference between silicon and transparent media is that the intensity saturation level in silicon is below the damage threshold.
